1. Field of the Invention
The present invention relates to load control systems for controlling the amount of power delivered to an electrical load, such as a lighting load or a motor load, from an alternating-current (AC) power source. More specifically, the invention relates to a load control device having a power supply and a controller, and operable to provide substantially all of a supply voltage of the AC power source to the electrical load.
2. Description of the Related Art
It is often desirable to include a lamp in the same enclosure as a fan motor. Since the lamp and the fan motor are often wired in parallel, the lamp and the fan motor are generally controlled together from a switch located remotely from the lamp and the fan motor. FIG. 1A shows a prior art light and fan motor control system 10. The system 10 includes a maintained switch 12 coupled between an alternating-current (AC) voltage source 14 and two loads: a fan motor 16 and a lighting load 18. The fan motor 16 and the lighting load 18 are connected in parallel such that when switch 12 is closed the fan motor 16 and the lighting load 18 will both be on, and when the switch 12 is open the fan motor 16 and the lighting load 18 will both be off.
There are also various schemes for independent control of a fan motor as well as a lighting load from a remote location such as a wallstation. FIG. 1B shows a prior art light and fan motor control system 20, having a dual light and fan speed control 22 coupled to the AC voltage source 14. The dual light and fan speed control 22 has two outputs: the first output coupled to the fan motor 16 and the second output coupled to the lighting load 18, to allow for independent control of the loads. Further, the dual light and fan speed control 22 includes a fan speed circuit for adjusting the speed at which the fan motor 16 turns and a dimmer circuit for changing the intensity of the lighting load 18. The dual light and fan speed control 22 is often mounted in a standard electrical wallbox and includes a user interface to allow a user to separately control the lighting load and the fan motor.
However, the dual light and fan speed control 22 requires two separate wires to be connected between the control and the loads, i.e., the lighting load 18 and the fan motor 16. If these two connections are not provided between the wallbox and the enclosure containing the lamp and the fan motor, independent control of the lighting load and the fan motor will not be possible. Further, in the system 20 of FIG. 1B, it is only possible to have one dual light and fan speed control 22, and thus, only one user interface to allow for adjustment of the light intensity and the fan speed. Control of the fan motor and lighting load from more than one location is not possible in this system.
Thus, it is desirable to provide a reliable means to independently control from a remote location a fan motor and a lighting load that are located in the same enclosure. Since a consumer may wish to locate the fan motor and the attached lamp in a position previously occupied by only a lamp controlled by a standard single-pole single-throw wall switch, it is desirable to be able to control the fan motor as well as the attached lamp independently, using a two-wire control device. A two-wire control device is a control device that has only two electrical connections (one connection to the AC voltage source and the other connection to the enclosure containing the lamp and the fan motor) and does not have a neutral connection. As shown in FIG. 1A, this kind of system typically only includes a switch in series electrical connection between the AC voltage source and the lamp/fan and no neutral connection is available in the electrical wallbox where the switch is housed. Since it is desirable to control the fan motor and the lamp independently, using the existing building wiring, it is necessary to develop a means to allow independent control over the existing building wiring consisting of a single pair of wires connecting the remote wallstation to the lamp/fan apparatus.
Such a remote wallstation preferably includes a microcontroller to receive inputs from a user interface and to communicate with a load control device in the enclosure of the lighting load and the fan motor. To power the microcontroller with a substantially direct-current (DC) voltage, the wallstation must also include a DC power supply.
Thus, there exists a need for a power supply for a two-wire load control device that passes as much of the voltage from the AC voltage source to the loads (or another load control device) as possible and derives a minimal amount of power from the AC voltage source to power a microcontroller and other low-voltage circuitry.